1. Filed of the Invention
This invention relates to a brake fluid pressure control apparatus for a vehicle which can prevent locking of the wheels or which can prevent locking of the wheels and also control the traction of the drive wheels on acceleration of the vehicle, as when the vehicle starts.
2. Description of the Prior Art
For example, U.S. Pat. No. 4395073 discloses a brake fluid pressure control apparatus in a skid control system for a vehicle having at least one wheel and a brake for the wheel which includes a fluid pressure control valve device arranged between a master cylinder and a wheel cylinder of a brake for the wheel. The fluid pressure control valve device receives control signals from a control unit measuring the skid condition of the wheel to control the brake fluid pressure to the wheel cylinder. A hydraulic reservoir reserves the brake fluid discharged through the fluid pressure control valve device from the wheel cylinder when the brake fluid pressure to the wheel cylinder is decreased with control of the fluid pressure control value device. A pressure fluid supply conduit connects the master cylinder with the fluid pressure control valve device and a fluid pump returns the brake fluid from the hydraulic reservoir into the pressure fluid supply conduit. A first check valve arranged in the pressure fluid supply conduit is opened when the brake fluid flows from the master cylinder toward the fluid pressure control valve device, and the outlet of the fluid pump is connected to the pressure fluid supply conduit between the first check valve and the fluid pressure control valve device. A pressure fluid return conduit connecting the master cylinder with the wheel cylinder and a second check valve arranged in the pressure fluid return conduit is opened when the brake fluid flows from the wheel cylinder toward the master cylinder, and a hydraulic accumulator or a fluid pressure adjusting valve receives the brake fluid discharged from the fluid pump.
With the above-described brake fluid pressure control apparatus, the wheels can be prevented from locking and kickback of the brake pedal can be avoided when the anti-skid control operator. However, since the hydraulic accumulator consists of a strong and heavy spring, a piston urged by the spring and a casing for the spring and piston, the whole apparatus is large-sized and heavy. It is very difficult to fit such an apparatus in a limited space such as the engine compartment of a vehicle.
On the other hand, the driving slip or traction control apparatus which can control or prevent the slip of the drive wheel vehicle acceleration with the increasing engine power, has been developed recently. This Applicant proposed a brake fluid pressure control apparatus which can prevent the wheels from locking and further control the drive wheels from slipping in the Japanese Patent Application No. 16732/1987. However, this apparatus is nearly equal to the arrangement in which the drive slip control apparatus is merely added to the lock preventing apparatus. As a result, the whole apparatus is large and heavy, and is accordingly costly.